Math 14 HW 6.4.5-T Using the Central Limit Theorem

If 1 adult female is randomly​ selected, find the probability that her pulse rate is less than 75 beats per minute. If 16 adult females are randomly​ selected, find the probability that they have pulse rates with a mean less than 75 beats per minute. Why can the normal distribution be used in part​ (b), even though the sample size does not exceed​ 30?